Low voltage ride-through strategy for a grid-forming converter with 3 times current overload based on adaptive virtual impedance

Introduction During three-phase faults in power grids, existing low-voltage ride-through (LVRT) strategies are often constrained by the current withstand capability of converters, resulting in insufficient voltage support. In addition, the widely used virtual impedance method involves complex calculations and difficult parameter selection under complex grid conditions. Methods To address these issues, this paper proposes a grid-forming adaptive virtual impedance LVRT strategy that matches the 3-time overload capability for 10 s specified in TCES243-2023. The proposed strategy determines the adaptive adjustment interval based on the relationship curves between the active and reactive components of the fault current and the virtual impedance. Furthermore, the calculation method of the active and reactive current reference values is redesigned by considering the 3-time overload capability. Through adaptive virtual impedance adjustment, the strategy ensures current limiting and reactive current injection while improving voltage support using the enhanced overload capability of grid-forming converters. Results Matlab/Simulink discrete electromagnetic transient (EMT) simulations with a sampling step of 10 μs were carried out to verify the effectiveness of the proposed strategy. The results show that the point of common coupling (PCC) voltage is supported to 311 V, corresponding to the rated value, under a 30% grid voltage sag; to 290 V under a 60% voltage sag; and from 31 V to 200 V under a 90% voltage sag. Compared with the 1.1-time overload scheme, the voltage support effect is more than doubled. Meanwhile, the fault current, including transient impact current, is limited within three times the rated current throughout the fault process. Discussion The proposed strategy effectively addresses the problems of difficult virtual impedance parameter selection and insufficient voltage support in traditional LVRT schemes. It improves the grid support capability of grid-forming converters under severe grid faults while satisfying current-limiting requirements.